It seems most of you were right on track with this one – probably because you can still buy such a device. This thingy launches a small ball horizontally while at the same time dropping a ball. It is supposed to show that the vertical and horizontal components of an object in projectile motion are independent.

It takes two balls (which I didn’t have when I took the picture). One ball goes on each end and the arm is pulled back.

Update: Thanks to Kevin and Frank for pointing out that my diagram was backward – I fixed it.

Maybe this diagram helps. This particular model has two speed settings for the launched ball. Oh, the dropped ball has a hole in it so that it fits on that piston. When the piston pushes the launched ball forward, the ball drops off. Maybe I should have made a quick video. Oh well.

Comments

You have got the two labels reversed. When the arm is pulled back and locked under tension, the left side is where you would put the ball to be launched, and the right side (which is now poking out) the ball with hole to be dropped.